There has been proposed the method for forming color images on a thermal transfer image-receiving sheet which is dyeable with a sublimation dye by using a thermal transfer sheet composed of the sublimation dye as a recording agent and a substrate on which the sublimation dye is supported. In this method, the dye is heated using a thermal head of a printer as a heating means and transferred on the image-receiving sheet to obtain the color images. The thus formed images are very clear and excellent in transparency because of the dye used, and are therefore expected to provide high-quality images which are excellent in reproducibility of half tones and gradation. For this reason, thermal transfer image-receiving sheets capable of exhibiting the above properties have been developed, and a polyester resin has been used as a dye receiving layer thereof.
Patent Literature (hereinafter referred to as PTL) 1 discloses a coloring matter receiving material for thermal sublimation printing which includes a coloring matter receiving layer containing a graft polymer composed of an unsaturated copolyester as a backbone and a vinyl copolymer as a superstrate, and a substrate, for the purpose of improving color density, clarity and sharpness of images, stability of images and adhesion to a coloring matter donating material.
PTL 2 discloses a polyester-based resin containing, as a main component, a graft polymer product having a glass transition temperature of 25° C. or higher and a molecular weight of from 0.15 to 1.5 in terms of a reduced viscosity which is in the form of a polymer composed of an unsaturated bond-containing polyester as a main chain and a polymer obtained from a radical polymerizable unsaturated monomer as a side chain, and a sublimation transfer image receptor having a dyeable layer composed mainly of a dyeable resin containing the polyester-based resin, for the purpose of improving an image-forming sensitivity.
PTL 3 discloses a polyester-based resin containing, as a main component, a graft polymer product having a tan δ peak temperature of 40° C. or higher and a glass transition temperature of 15° C. or higher, and a molecular weight of from 0.15 to 1.5 in terms of a reduced viscosity which is in the form of a polymer composed of an unsaturated bond-containing polyester as a main chain and a polymer obtained from a radical polymerizable unsaturated monomer as a side chain, and a sublimation transfer image receptor having a dyeable layer composed mainly of a dyeable resin containing the polyester-based resin, for the purpose of improving dyeing sensitivity, durability of images and storage stability.
PTL 4 discloses a thermal transfer image-receiving sheet which includes a substrate and a dye receiving layer formed on the substrate which contains a graft polymer composed of at least one monomer selected from an acrylic monomer and a methacrylic monomer and at least one polyester, for the purpose of improving a printing density, adhesion of the laminated film, bleeding and discoloration of images and traveling stability.
PTL 5 discloses a receiving layer composition for thermal transfer image-receiving sheets which includes a resin containing a polyester obtained by polycondensing an alcohol component containing an alkyleneoxide adduct of bisphenol A in an amount of 50 mol % or more and a carboxylic acid component containing an alicyclic carboxylic acid in an amount of more than 50 mol %, and a polyether-modified silicone having an oxyethylene group and/or an oxypropylene group, for the purpose of improving dyeability and releasability.
PTL 6 discloses a dye receiving layer composition for thermal transfer image-receiving sheets which includes a resin containing a polyester obtained by using an alcohol component containing an alkyleneoxide adduct of 2,2-bis(4-hydroxyphenyl)propane in an amount of 50 mol % or more, and an oxazoline group-containing compound, for the purposes of improving dyeability with dyes and releasability from a transfer sheet and attaining an excellent transfer image performance.
PTL 7 discloses a thermal transfer image-receiving material which includes a substrate and at least one image-receiving layer formed on the substrate which receives a coloring matter transferred from a thermal transfer coloring matter donating material upon heating to form an image thereon and which is formed of a composition prepared by dispersing a coloring matter receiving substance in a water-soluble binder, wherein an uppermost layer of image-receiving surface-forming layers of the image-receiving material contains a co-dispersed material composed of a silicone compound and a plasticizer having an [organic/inorganic] ratio of 1.5 or more, for the purpose of improving film properties and a transferred image density.